How can an std::ostream be moved?

Since it is by design that std::ostream can't be moved the question becomes: how can an std::ostream be moved such that it can write to different destinations?

The basic objective is to have a factory function taking a URI and returning something, let's call it, omstream (output movable stream) which can be used like an std::ostream:

omstream stream_factory(std::string const& uri);
void     process(std::ostream& out);

int main(int ac, char* av[]) {
    omstream destination{ stream_factory(ac == 2? av[1]: "example.txt") };
    process(destination);
}

The omstream would be responsible for properly moving the object:

class omstream
    : public std::ostream {
    // suitable members
public:
    omstream(/* suitable constructor arguments */);
    omstream(omstream&& other) // follow recipe of 27.9.1.11 [ofstream.cons] paragraph 4
        : std:ios(std::move(other))
        , std::ostream(std::move(other))
        // move any members {
        this->set_rdbuf(/* get the stream buffer */);
    }
    // other helpful or necessary members
};

The question is really what it takes to implement omstream (or, even a corresponding class template basic_omstream)?